The term "heavy oil" as used herein means a hydrocarbon oil containing heavy components having boiling points of about 650.degree. F. (343.degree. C.) and higher. Such heavy oils include various crude oils; non-distillates such as atmospheric distillation residues and vacuum distillation residues of such crude oils; solvent-deasphalted oil; solvent-deasphalted oil asphalt; shale oil; tar sand oil; liquefied coal oil; distillates such as HGO (topped heavy gas oil) and VGO (vacuum gas oil); and blends of these distillates and the above-described non- distillates.
A variety of methods are known for obtaining lighter products by cracking a heavier oil. One such method is fluidized catalytic cracking (FCC). A great deal of research has been conducted in FCC to achieve high yields and selectivity. One method for improving the yield of light oil is to use a mixture of an additive that acts to promote the cracking of heavy components in heavy oil, with a conventional cracking catalyst.
Typical FCC catalyst additives include alumina, clay and silica, particularly wherein the ratio of strong acidity to the total acidity is high. Consequently, such additives are accompanied by problems such as the cracking of heavy oil is not adequately promoted, or excessive coke is deposited on the catalyst. Further, additives composed of a composite oxide such as silica-alumina, clay and silica are also known to be effective for the promotion of cracking of heavy oil and for the suppression of deposition of coke. However, they do not make it possible to reduce the ratio of strong acidity to total acidity to or beyond a certain value, and therefore involve problems that a cracking reaction proceeds too much to increase the proportion of naphtha in the cracked product.
An object of the present invention is therefore to provide an additive catalyst for the cracking of heavy oil which: has high cracking activity for heavy components in the heavy oil; which features reduced coke deposition; and which brings about a high naphtha yield.
With a view to attaining the above-described object, the present inventors have proceeded with extensive research, leading to the completion of the present invention.
According to the present invention, there is thus provided an additive catalyst for the cracking of heavy oil (Catalyst I), characterized in that the additive catalyst comprises: (i) a mixed metal oxide composed of an acidic metal oxide and a basic metal oxide, in which the proportion of the basic metal oxide is from 5 to 50 mole %, (ii) clay, and (iii) silica.
The present invention also provides an additive catalyst for the cracking of heavy oil (Catalyst II), characterized in that the additive catalyst comprises: (i) an acidic metal oxide other than silica, or an acidic mixed metal oxide, (ii) clay, (iii) silica, and (iv) a basic metal oxide.
In addition, the present invention further provides an additive catalyst for the cracking of heavy oil (Catalyst III), characterized in that the additive catalyst comprises: (i) an acidic metal oxide other than silica, or an acidic mixed metal oxide, (ii) clay, (iii) silica, and (iv) basic metal cations.